The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element.

Return Value

An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

Type Parameters

TSource

The type of the elements of source.

TCollection

The type of the intermediate elements collected by collectionSelector.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

The SelectMany<TSource, TCollection, TResult>(IEnumerable<TSource>^, Func<TSource, Int32, IEnumerable<TCollection>^>^, Func<TSource, TCollection, TResult>^) method is useful when you have to keep the elements of source in scope for query logic that occurs after the call to SelectMany<TSource, TCollection, TResult>(IEnumerable<TSource>^, Func<TSource, Int32, IEnumerable<TCollection>^>^, Func<TSource, TCollection, TResult>^). See the Example section for a code example. If there is a bidirectional relationship between objects of type TSource and objects of type TCollection, that is, if an object of type TCollection provides a property to retrieve the TSource object that produced it, you do not need this overload of SelectMany<TSource, TCollection, TResult>(IEnumerable<TSource>^, Func<TSource, Int32, IEnumerable<TCollection>^>^, Func<TSource, TCollection, TResult>^). Instead, you can use SelectMany<TSource, TResult>(IEnumerable<TSource>^, Func<TSource, Int32, IEnumerable<TResult>^>^) and navigate back to the TSource object through the TCollection object.